Dwelling on past keeps dude disheartened (9)
I believe the answer is:
residence
'dwelling' is the definition.
(thesaurus)
'on past keeps dude disheartened' is the wordplay.
I cannot quite understand how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for residence that I've seen before include "bode" , "Dire scene (anag.)" , "Person's home" , "The White House" , "Dwelling place" .)